Đáp ứng biên độ của bộ lọc số thông thấp lý tưởng được định nghĩa

$\left|H\left(e{}^{j\omega }\right)\right|=\{\begin{array}{c}1\\ \text{v}\text{o}\text{i}\omega \\ 0\\ \text{v}\text{o}\text{i}\omega c{}^c\left(-\pi \le \omega \le \pi \right)\end{array}$

$\left|H\left(e{}^{j\omega }\right)\right|=\{\begin{array}{c}1\\ \text{v}\text{o}\text{i}\omega \\ 0\\ \text{v}\text{o}\text{i}\omega c\left(-\pi \le \omega \le \pi \right)\end{array}$

$\left|H\left(e{}^{j\omega }\right)\right|=\{\begin{array}{ccc}\hfill 1\hfill & \hfill \text{v}\text{o}\text{i}-\omega {}_c\le \omega \hfill & \hfill 0\hfill \\ \hfill \text{v}\text{o}\text{i}\omega \hfill & \hfill 0\hfill & \hfill c{}_1\hfill \end{array}|-\frac{\pi }{2}\le \omega \pi$

$\left|H\left(e{}^{j\omega }\right)\right|=\{\begin{array}{c}1\\ \text{v}\text{o}\text{i}-\omega {}_c\le \omega \\ 0\\ \text{v}\text{o}\text{i}\omega c{}_1\left(-\pi \le \omega \le \pi \right)\end{array}$